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#include <cmath>
#include <filesystem>
#include <fstream>
#include <iostream>
#include <tuple>
#include <vector>
using namespace std;
namespace {
class UnionFind {
public:
explicit UnionFind(size_t size)
: parent_(size)
, size_(size, 1)
{
for ( size_t i = 0; i != size; ++i ) {
parent_[i] = i;
}
}
size_t find(size_t n)
{
if ( parent_[n] != n ) {
parent_[n] = find(parent_[n]);
}
return parent_[n];
}
bool unite(size_t a, size_t b)
{
a = find(a);
b = find(b);
if ( a == b ) {
return false;
}
if ( size_[a] < size_[b] ) {
swap(a, b);
}
parent_[b] = a;
size_[a] += size_[b];
return true;
}
[[nodiscard]]
vector<size_t> get_component_sizes() const
{
vector<size_t> sizes;
for ( size_t i = 0; i != parent_.size(); ++i ) {
if ( parent_[i] == i ) {
sizes.emplace_back(size_[i]);
}
}
return sizes;
}
private:
vector<size_t> parent_;
vector<size_t> size_;
};
using Pos = tuple<long, long, long>; // (x, y, z)
using Dist = tuple<double, size_t, size_t>; // (Distanz, Von, Nach)
vector<Pos>
read_file(const filesystem::path& filename)
{
ifstream file{ filename };
vector<Pos> list;
long x{};
long y{};
long z{};
char ch{};
while ( file >> x >> ch >> y >> ch >> z ) {
list.emplace_back(x, y, z);
}
return list;
}
double
get_distance(const Pos& pos1, const Pos& pos2)
{
const auto [x1, y1, z1] = pos1;
const auto [x2, y2, z2] = pos2;
return hypot(x1 - x2, y1 - y2, z1 - z2);
}
vector<Dist>
get_distances(const vector<Pos>& list)
{
// Distanzen paarweise erfassen...
vector<Dist> dists;
for ( size_t i = 0; i != list.size(); ++i ) {
for ( size_t j = i + 1; j != list.size(); ++j ) {
dists.emplace_back(get_distance(list[i], list[j]), i, j);
}
}
// ... und nach Distanz sortieren
ranges::sort(dists);
return dists;
}
void
part1(const vector<Pos>& list)
{
const auto dists = get_distances(list);
UnionFind unionFind(list.size());
// die nächsten 1000 Paare verbinden
for ( size_t i = 0; i != 1000; ++i ) {
const auto [dist, a, b] = dists[i];
unionFind.unite(a, b);
}
auto sizes = unionFind.get_component_sizes();
// Sortieren
nth_element(sizes.begin(), sizes.begin() + 3, sizes.end(), greater<>());
cout << "Part 1: " << sizes[0] * sizes[1] * sizes[2] << '\n';
}
void
part2(const vector<Pos>& list)
{
const auto dists = get_distances(list);
UnionFind unionFind(list.size());
// Alle Paare verbinden ...
size_t unions = 0;
for ( auto [dist, a, b]: dists ) {
if ( unionFind.unite(a, b) ) {
// ... beim Letzten abbrechen
++unions;
if ( unions == list.size() - 1 ) {
cout << "Part 2: " << get<0>(list[a]) * get<0>(list[b]) << '\n';
return;
}
}
}
}
} // namespace
int
main()
{
auto data = read_file("data/day08.txt");
part1(data);
part2(data);
}
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